Don't buy one off a pikey or anybody that looks like one
Usually if you get talking to the person who is selling the boat or item you can get a good idea if their genuine or not?
off coarse that person who is selling you the boat in good faith may of bought the boat off somebody who wasn't without knowing about it, so i guess you can't always tell? you could ask the person who is selling the boat if they don't mind you doing a hull identification check before you purchase the boat and see how easy they are about it, also ask for paperwork or receipts if any. But at the end of the day buying a boat is not like buying a car where you have reg numbers and a registration document to prove ownership, maybe it should be i don't know? but ribs are very desirable items and are targeted by organized thieves.
this debate has no doubt been discussed before on the forum so do a search.